1. Field
A certain aspect of the embodiment disclosed herein relates to a video decoding device and a video decoding method for decoding video data that includes a plurality of pictures, one of which is encoded by referencing another.
2. Description of the Related Art
Video decoding devices have been used to decode video data that was encoded to reduce the amount of data. However, in some cases, a video decoding device cannot acquire some of video data. For example, a television receiver or a mobile terminal that receives encoded video data distributed using radio waves and decodes the video data may fail to receive some of the video data due to the condition under which the radio waves are received. In such a case, the video decoding device cannot correctly decode a picture corresponding to the unreceived and lost data. In particular, when video data is encoded using an inter coding method in which a picture is encoded using information regarding the previous and next pictures, the video decoding device cannot decode a picture that refers to the picture corresponding to the lost data as well.
Accordingly, an error concealment technology has been developed. In error concealment technology, a pseudo picture or a pseudo area is reconstructed for an error picture or an error area of a picture corresponding to lost data using the information regarding an area of a non-lost picture or a non-lost picture.
For example, Japanese Laid-open Patent Publication No. 2006-203598 describes a digital image decoding apparatus that determines whether an image is a panned image and detects an error block that includes an error. When the digital image decoding apparatus determines that a target image is a panned image and if the digital image decoding apparatus detects an error block, the digital image decoding apparatus generates a motion vector for motion compensation for the error block on the basis of motion vectors of a plurality of normal blocks located in the vicinity of the erroneous block. Alternatively, Japanese Laid-open Patent Publication No. 2007-325206 describes a video decoding device that determines the validity of macroblocks located in the vicinity of a macroblock to be recovered. Thereafter, the video decoding device acquires context information for image recovery from the nearby macroblocks that have been determined to be valid and computes an estimated motion vector used for recovering the macroblock to be recovered. Subsequently, the video decoding device acquires a decoded image from a decoded frame using the computed motion vector and generates a recovered image.
In these error concealment technologies, in order to determine areas of a picture used for concealing an area having an error, a motion vector that indicates an area of a different picture including an image similar to the image of the areas in the vicinity of the area having an error is used. Accordingly, in such error concealment technologies, if a motion vector of an area in which an error occurred is correctly estimated, the area in which an error occurred may be generated by interpolating an image similar to an original image in the area.
However, the motion of an image in an area in which an error occurred frequently differs from the motion of an image in an area in the vicinity of the area in which an error occurred. Therefore, in such error concealment technologies, in some cases, it is difficult to correctly estimate the motion of the image in the area in which an error occurred. In particular, when an area in which an error occurred is large and, therefore, the area includes a plurality of macroblocks used for estimating the motion vector, images in the macroblocks included in the area in which an error occurred may move in different directions. Accordingly, the image in an error concealment area may not match the images in areas in the vicinity of the error concealment area and, therefore, the image quality of a picture including the error concealment area may be significantly decreased.